A conflict monitor is an electronic apparatus which is connected to a traffic controller. A traffic controller is a familiar apparatus which controls traffic lights at an intersection. The typical traffic controller comprises a plurality of electronic or electromechanical switches each of which is operated by a timing mechanism, such as a clock. The clock is pre-programmed so that it activates, for example, a green light in one direction for a predetermined period of time, then activates the yellow light in that direction, and then the red light. When the controller activates a green light in one direction, it also activates red lights in intersecting, or conflicting directions. The conflict monitor receives input signals indicating which lights have been activated and performs various logic operations on these signals. The definition of a "conflict" can vary, but is at a minimum defined as green signal indications being provided to intersecting lanes of traffic. In addition, a conflict monitor may measure the duration of the green, yellow or red lights and indicate a fault if these durations meet or exceed predetermined time periods. The "walk" and "don't walk" signals may be considered in a manner similar to that of the colored traffic signals so that a "conflict" may include such errors as providing a "walk" signal across a lane of traffic receiving a green light.
When the conflict monitor determines the existence of an error, it typically activates a relay which causes all lights in the intersection to be flashing red or flashing yellow.
Various conflict monitors are known in the prior art. U.S. Pat. No. 3,629,802 (Clark, et al.) shows a conflict monitor employing a number of logic elements interconnected to produce an output when conflicting right-of-way command signals are coincident. U.S. Pat. No. 3,778,762 (Jarko, et al.) uses a plurality of logic elements to detect conflicts between traffic signals. This monitor uses optically-coupled sensors, with the output of each sensor being directed to at least one logic element. U.S. Pat. No. 3,902,156 (Hill) teaches a conflict monitor wherein each input is connected to an AC-to-DC converter, and the input of this converter is applied to individual logic elements which are interconnected to detect various conflicts. U.S. Pat. No. 4,135,145 (Eberle) teaches a conflict monitor wherein the outputs of traffic control switches are inputs to fault detectors which comprise a plurality of logic elements arranged to effect a predetermined logical operation.
U.S. Pat. No. 4,383,240 (Staats, Jr.) teaches a device for storing and visually displaying the operational state of a traffic control system. This allows the status of any input to be indicated as of the time of the occurrence of an error.
It is also known to measure voltage of a signal by taking time-spaced samples. U.S. Pat. No. 4,077,061 (Johnston, et al.) shows a circuit for measuring electrical energy wherein voltage and current are randomly sampled and converted to respective binary representations. These binary representations are then processed to produce a visual display of the electrical energy. U.S. Pat. No. 3,984,737 (Okamura, et al.) also teaches measurement of instaneous voltage and current and uses a computer to determine the product of these values. Values determined at previous times are added to the present value to eliminate unnecessary frequency components. U.S. Pat. No. 4,240,149 (Fletcher, et al.) shows a circuit for measuring a parameter which is an integral with respect to time. A variable is sampled at a frequency asynchronous with that of the variable, and the sampled values are periodically summed to provide an indication of the interval.
Multiplex devices for use in digital circuits are also known, such as that shown in U.S. Pat. No. 4,307,392 (Loshbough, et al.). This patent shows a scanning circuit for causing signals in storage registers to be transmitted to a pre-programmed ROM.